The present invention relates to a flame-retardant polyamide resin composition for use in electronic/electrical parts, automotive electrical equipment parts, etc.
Polyamide resins with excellent heat-resistance, mechanical properties, and moldability are utilized for parts in various industrial fields. When the resins are used for such application, it is often required to render them flame-retardant. Flame retardants, such as halogen compounds, metal hydroxides, nitrogen compounds, and phosphorus compounds, have been used for such purpose. However, use of halogen compounds causes environmental pollution by dioxin, etc., and generates toxic combustion gases, use of metal hydroxides has insufficient flame-retarding effect, and use of nitrogen compounds may result in inferior flame-retardancy of the resin when an inorganic filler is added.
The flame-retardant composition comprising melamine phosphate disclosed in JP Patent Appln. Disclosure No. 53-49054/78 generates volatiles when injection-molded, which staining the mold and impairing the appearance of the molded product.
As flame-retardant composition the flame-retardancy of which is not reduced even when an inorganic filler is compounded with the polyamide resin, and by which only a relatively small amount of volatiles is generated under injection molding, there is disclosed in JP Patent Appln. Disclosure No. 10-505875/98 a flame-retardant glass fiber-reinforced polyamide resin composition prepared by addition of a melamine- or melem-phosphoric acid reaction product or a mixture thereof to a polyamide resin. A relatively large amount of flame-retardant must be added for the purpose of endowing the composition with flame-retardancy of grade V-0 in the UL94 flammability test, performed by using a 1.6 mm ({fraction (1/16)} in.) thick test piece. If the flame-retardancy of the composition is to be increased to the level of grade V-0 in said test when using a 0.8 mm ({fraction (1/32)} in.) thick test piece, the amount of flame-retardant to be added must be further increased, and the increase causes staining of the mold under injection molding.